sigma 30mm f1.4 infinity focus

[wind30]

I just got a piece of sigma 30mm f1.4 lens.

I noticed something about this lens is when shooting at f1.4 for objects at infinity, it is REALLY hard to get consistent good focus using the AF on my E330.

The lens is very sharp at f1.4 WHEN you have a perfect focus but most of the time, it misses focus.

For nearer objects the focusing seems to be more accurate. I searched the net and found that this seems to be a common issue for the lens.

Should I bring it down to sigma and see if they can get it fixed? Other than the missed focus at infinity, I am pretty happy with this lens as it is really sharp. I don't want the sigma singapore to mess it and ended with a worse lens if this problem can't be fixed. Especially I seldom shoot at f1.4 for objects at infinity...

[lsisaxon]

Originally Posted by wind30 I just got a piece of sigma 30mm f1.4 lens. I noticed something about this lens is when shooting at f1.4 for objects at infinity, it is REALLY hard to get consistent good focus using the AF on my E330. The lens is very sharp at f1.4 WHEN you have a perfect focus but most of the time, it misses focus. For nearer objects the focusing seems to be more accurate. I searched the net and found that this seems to be a common issue for the lens. Should I bring it down to sigma and see if they can get it fixed? Other than the missed focus at infinity, I am pretty happy with this lens as it is really sharp. I don't want the sigma singapore to mess it and ended with a worse lens if this problem can't be fixed. Especially I seldom shoot at f1.4 for objects at infinity...

Is it a front/back focus issue? If so, then call up Sigma to make an appointment. You'll need to bring your body down with the lens. They will take a few shots with the body and then reprogram the chip in the lens. It's probably for backlash correction.

My 24/1.8 had a 25mm front focus issue, now it's spot on after the calibration.

[wind30]

can you get the lens back immediately?

[lsisaxon]

Originally Posted by wind30 can you get the lens back immediately?

If you make an appointment, you will get it back on the spot. Since it's a prime lens, it should take no more than an hour to do the calibration. Unless your lens does not have a programmable chip, then they will need to import a chip from Japan, that will take longer.

[kelccm]

One question. Why is it only hard to achieve focus when the lens was set to f/1.4 aperture? I thought all lenses will focus at wide open aperture no matter what aperture you set?

[lsisaxon]

Originally Posted by kelccm One question. Why is it only hard to achieve focus when the lens was set to f/1.4 aperture? I thought all lenses will focus at wide open aperture no matter what aperture you set?

I believe it's a front/back focus issue and at f/1.4, the DoF is so shallow that slight misfocus is very evident.

I also thought if the AF sensor is ok in the body, any lens should focus correctly. Apparently not. My Sigma 24/1.8 consistently focuses 25mm short of the target until it was sent for calibration. I could even see the focus is off from the focusing screen. I think it might be because of backlash setting in the lens that asks the body to turn a little bit more when the focus hits.